Reduction of the swelling index of regenerated cellulose fibers by steam under pressure



Patented Aug. 26, 1952 REDUCT IO N THE SWELIuING INDEX OF REGENERATED CELLULOSE FIBERS BY STEAM UNDER Nicolas Drisch and AndrBonnet, Paris, France, I V assignors to Comptoir des Textiles Artificiels, a

corporation of France No Drawing. Application February 15, 1951-, Serial No. 211,195. In France April 21,1944

2 Claims.

This invention relates to a new and improved process of treatin absorbent textile fibers and to the product resulting therefrom. More particularly, it relates to substantially reducing the hygroscopicity of regenerated cellulose staple fibers and the product resulting therefrom.

This application is a continuation-in-part of our co-pending application for Process of Treating Absorbent Textiles, Serial No. 723,902, filed J anuary23, 1947 now abandoned.

Hygroscopicity is herein defined as the index of swelling and is determined as follows: The cellulose material; after being saturated with water, as by dipping in water, is centrifuged for minutes in a centrifugal drier-3D centimeters in diameter and rotating at 3000 R. P. M. .The index of swelling is the weight of the water re tained by the centrifuged material compared with the original dry material.

U. S. Patent No. 1,544,885 to Brandenberger discloses a process of reducing the hygroscopicity of cellulose hydrates, and particularly regenerated cellulose, by subjecting such material in its dry state to the action of dry saturated steam, preferably under pressure, in a closed vessel. Such a process will reduce the swelling index of regenerated cellulose having a swelling index of between 80% and 150% to 50% or below.

In addition to the reduction in hygroscopicity, the treated product acquired other beneficial results: The shrinkage determined by the decrease in the dimensions resulting from washing with water, followed by drying without tension, of the steam-treated cellulose materials, such as pellicles, fibers, threads or fabrics made therefrom, was materially lower than that which characterized the untreated cellulose material.

2 However, the process of the Brandenberger Patent No. 1,544,885 possessed a serious disadvantage in that the cellulose subjected to the process underwent a depolymerization which Was manifest as a deterioration in the mechanical properties and which produced a yellowing of the product. I An object of this invention is to. provide a method of substantially reducing the swelling index of regenerated cellulose staple fibers without any appreciable depolymerization of the cellulose.

A further object of the invention is to provide a method of treating regenerated cellulose textile materials to materially reduce their swellingindex without affecting their serimetric properties.

Other and additional objects will bccome ap parent hereinafter;

4 ity of treatment.

This is avoided in accordance with the present invention by means of a two-stage steam treatment in which the mass of fibers is placed in a closed vessel which is evacuated to remove any air or gases from the interior of the mass which 7 would interfere with the freepassageof the steam thereto. Dry saturated steam is thus introduced into the vessel until theinterior is brought up to the steam pressure. Since the steam penetrates rapidly the entire mass isbrought up to treating temperature before substantial condensation can occur. However, in order to remove even this small amount of condensation the steam is again shut off, the vessel evacuated, and the operation repeated. Since the mass is then heated, no condensation occurs. The steam treatment under pressure then continues for a predetermined period after which the steam is shut ofi and the vessel opened to remove the treated fibers.

The details and manner of practicing the invention will become apparent by reference to the following specific example, it being understood that this example is merely illustrative of an embodiment of the invention and that the scope of the invention is not restricted thereto.

Example One or more 200 pound bales of staple fibers of regenerated cellulose obtained by either the viscose or cuprammonium processes is placed in a large autoclave or is formed into a ball which is placed in such autoclave. After closing the autoclave it is subjected to vacuum of from 5 centimeters to 10 centimeters of mercury. Dry saturated steam of a pressure of from 1.8 to 2 kg. per square centimeter is then introduced until the pressure in the autoclave is brought up to the steam pressure. The steaming is continued a few minutes to bring the entire mass up to the steam temperature. The steam is then shut off and the autoclave again evacuated as before to from 5 to 10 centimeters of mercury to remove all of the moisture from the: fibers, after which the steam is again introduced and crease; in elongation. tioni's due simply to the. shrinkage produced in the courseofth treatment andis not due .to any I Degree-or Eohimcri gwemltgl zation Index- Emma Untreated fibers Wil a; BZQ; 105; Treated fibers 320 58 The process is carried out with. dry saturated steam under a pressure which mayvary between 1.5 and 15 kg. per square centimeter and. at. the corresponding temperature. In general, a higher pressure. requires a shorter treatment and alower pressure. requires. a. longer treatment; For example, when a pressure. of. 1d kg. per square centimeter isv utilized, a treatment of several minutes is sufficient while with apressure of 1 kg.

per square centimeter a treatment of approximately a hours is. necessary. In the preferred embodiment pressures of. from. 1.8 to 2.0' kg. per square centimeter for a period. of 2 to 2' hours are. employed.

The process. reduces the. swelling index, and

7 hence the absorptive power of regenerated cellulose. textile-materials, without changing the. degree of polymerization. of. they original cellulose.

As aresnla the serlmetricv properties of the textilesv are. not. diminished in the least. In certain cases the. tenacity oi regenerated cellulose rayon yarn. is slightly reduced. However, such slight reduction in tenacity is. compensated by an in- Thisincrease in elongadeterioration. of the cellulose material. The

4 process additionally results in a product having improved (low) shrinkage and a yellowing considerably less than that of the prior art.

Since it is obvious, that. various. changes and modifications may be made in the above description without departing from the nature or spirit thereof, this invention is not restricted thereto except as set forth in the appended claims.

What; is claimed is:

1. Amethod. o'f'materially reducing the hygroscopie-ity' oi" regenerated cellulose staple fibers without... substantially changing their degree of polymerization; which comprises disposing a bale of. said. fibers. in-a closed vessel, evacuating the atmosphere in said vessel, then from an outside source introducing dry saturated steam under a pressure of from 1.5 to 15 kg. per sq. cm. into said. vessel until the interior of said vessel is brought up to the steam pressure and the mass is heatedthroughout then shuttingv ofi the steam andagain evacuating, the interior of said vessel, again introducing said steam into said vessel. to bring. the interior ofsafd vessel up to steam pressure of. the entering steam and maintaining said steam pressure in..said. vessel for a period 01 a few minutes to four hours, the time varying inversely as. the pressure.v

2. The method as claimed in claim 1 wherein the evacuation. is carried to between 5 centimeters and 10; centimeters of' mercury.

NICOLAS DRISCH. ANDRE. BONNET.

Number Name Date 1,544,885 Brandenherger July 71, 1925 2,119,261 Andrews"... May 31,, 1938 

1. A METHOD OF MATERIALLY REDUCING THE HYGROSCOPICITY OF REGENERATED CELLULOSE STAPLE FIBERS WITHOUT SUBSTANTIALLY CHANGING THEIR DEGREE OF POLYMERIZATION, WHICH COMPRISES DISPOSING A BALE OF SAID FIBERS IN A CLOSED VESSEL, EVACUATING THE ATMOSPHERE IN SAID VESSEL, THEN FROM AN OUTSIDE SOURCE INTRODUCING DRY SATURATED STEAM UNDER A PRESSURE OF FROM 1.5 TO 15 KG. PER SQ. CM. INTO SAID VESSEL UNTIL THE INTERIOR OF SAID VESSEL IS BROUGHT UP TO THE STEAM PRESSURE AND THE MASS IS HEATED THROUGHOUT, THEN SHUTING OFF THE STEAM AND AGAIN EVACUALING THE INTERIOR OF SAID VESSEL AGAIN INTRODUCING SAID STEAM INTO SAID VESSEL TO BRING THE INTERIOR OF SAID VESSEL UP TO STEAM PRESSURE OF THE ENTERING STEAM AND MAINTAINING SAID STEAM PRESSURE IS SAID VESSEL FOR A PERIOD OF A FEW MINUTES TO FOUR HOURS, THE TIME VARYING INVERSELY AS THE PRESSURE. 